Free curing rubber composition

ABSTRACT

A vulcanizable rubber is modified by the addition of a resin at a temperature above the melting point of said resin. Shaped articles are formed from the resulting blend and cured without restraining pressure at a temperature below the melting point of said resin. The resin portion is present in said articles in the form of particles having a cross sectional dimension (D) not greater than 1/2 micron and a length (L) to cross sectional dimension (D) ratio of 2 or greater.

This application is a continuation-in-part of U.S. application Ser. No.290,909, filed Sept. 21, 1972, now abandoned which is a DivisionalApplication of Ser. No. 66,753 filed Aug. 25, 1970, now U.S. Pat. No.3,701,702.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to preparation of a free cured vulcanizatecomprising a modified elastomeric composition. More specifically, theinvention relates to a vulcanizate prepared from a rubber-resin blendwherein the resin particles which are dispersed in the rubber have acertain shape with the result that the necessity for restrainingpressure to prevent blowing during the cure cycle of an article shapedfrom said blend is eliminated.

2. Description of the Prior Art

Presently, the blowing of rubber articles during or after cure (theterms "cure", "vulcanize" and variations thereof are used hereininterchangeably) is prevented by the application of restraining pressureon the article being cured through the use of platens, mold forms orother suitable restraining means. The blowing phenomenon occurs becauseone or more of the organic or inorganic compounds which are purposely orinadvertently compounded into rubber vaporize or expand when heatedduring the curing step of the fabrication process. As a result thestructure of the rubber is altered from a continuous solid to a cellularor spongy state.

Temperature and pressure are two important parameters when consideringthe vulcanization of any given rubber product. Because it iseconomically advantageous to have the fastest possible cures of rubberproducts when the product is held under restraining pressure, thetemperature chosen is usually the highest possible temperatureconsistent with the production of goods of satisfactory quality.

However, when rubber products are cured without pressure, or at arelatively low pressure, it has been determined that the maximumtemperature which can be employed in the curing step is limited by thetendency of most rubbers to blow during the cure, resulting in anundesirable porous article. The need for restraining pressure on therubber product during the curing cycle frequently necessitates theaddition of a separate step to the process as well as adding substantialexpense to the overall cost of the product since curing equipmentcapable of exerting restraining pressure must be provided.

Among others, two ways in which the prior art sought to eliminate theblowing during cure are: (1) to remove the substances which wouldvaporize (i.e. the volatiles) in the rubber, or (2) to use rubberspossessing high green strength.

To remove the volatiles contained in a compounded rubber, the rubberproduct is heated to a relatively low temperature in a dry vacuum priorto the curing step. This method also necessitates additional costlyequipment on the production line and is time-consuming.

The use of rubbers possessing high green strength eliminates the blowingphenomenon during the curing cycle because the uncured rubbercomposition has the inherent strength to withstand the bubble formationand expansion which generally results from the formation of entrappedgases, thus keeping them in solution in the rubber. The major drawbacksin this approach are that only a limited number of rubber polymerspossess the necessary internal strength to withstand blowing, andfurther, the modulus of these rubber polymers is such that theircommercial uses are somewhat limited.

DESCRIPTION OF THE INVENTION

The vulcanizate of the present invention is obtained by adding tonatural rubbers, synthetic rubbers or blends thereof, between about 2and 30% (based on total weight of the composition) of a fiber-forming,semi-crystalline, thermoplastic resin, said resin being dispersed insaid rubbers noted above in the form of particles having a crosssectional dimension not greater than one-half micron and a L/D (lengthto cross sectional dimension) ratio of 2 or greater. The blend is formedinto an article and cured at a temperature above 220°F. and at apressure below the water vapor pressure for the curing temperature. Thedensity of said cured article is not decreased by more than 3% of thedensity of the uncured rubber blend. The process for making thevulcanizate of the present invention comprises the following steps:

A. Initially, the rubber and resin in the amounts indicated above, alongwith pigments, fillers, antioxidants if desired, etc. forming thecomposition are blended in suitable mixing means, such as an internalshear (Banbury) mixer of a mixing mill, which is maintained at atemperature above the melting point of the thermoplastic resin. The hightemperature during this blending step insures a substantiallyhomogeneous dispersion of the resin and additives in the rubber.

Alternatively, another convenient way to blend the rubber-resincomposition is to prepare a masterbatch by blending rubber and resin ata ratio of from between about 1:1 to 3:1 respectively, at a temperatureabove the melting point of the resin, and subsequently blend the properamount of the resultant masterbatch into the unmodified rubber at atemperature near the melting point of the resin to result in acomposition containing between about 2 and 30% resin, based upon totalweight of composition.

B. After blending by either method described above, the rubber-resinmixture is cooled to a temperature below the melting point of the resin,for example, to about room temperature, whereupon; compositions

C. the blend is placed on a second mill which is maintained at atemperature low enough to prevent scorch, (e.g., about 200°F.) and theactive chemicals such as curatives, activators, antioxidants,accelerators, etc., are added to the blend and incorporated therein.

D. The resultant blend is formed into a shaped article using suchfabrication methods as molding, calendering, laminating, extruding orany combination thereof at a temperature below the melting point of thethermoplastic resin.

E. The shaped article is then free cured at a temperature below themelting point of the thermoplastic resin component in the blend andgenerally above 220°F. It is essential that the temperature of the blendat the shaping and curing stages of the process be below the meltingpoint of the thermoplastic resin contained therein.

The advantages resulting from the use of the present invention are that:

1. The rubber material is easier to feed to the extruders.

2. Blowing of the rubber during the curing cycle is eliminated as aprocessing problem, and consequently it is not necessary to cure theshaped rubber article under pressure in a mold.

3. Present or shorter press cycles for forming can be obtained at lowertemperatures with a free cure being completed at atmospheric pressureoutside of the mold. The expression "free cure" as used herein means thecuring of a shaped rubber article in a fluid medium at atmosphericpressure with little or no restraining means being used to preventblowing during the cure. If pressure is utilized for any reason duringthe cure cycle in the practice of the present invention, such pressureshall be substantially below (e.g., 1/2) the water vapor pressure of thecuring temperature, and the use of the aforesaid amount of pressure orless, shall be considered within the scope of the present invention as afree cure.

4. The rubber possesses better flow properties as a result of the use oflower levels of accelerators thus eliminating scorching. (Scorching is apartial cure of rubber before it has been shaped to the desired form.Scorching is attributable to the use of high levels of accelerators inthe rubber recipe in order to shorten the cure cycle time. The use ofhigh levels of accelerators increases the possibility that somevulcanization will occur during the blending and forming operationsprior to use).

The vulcanizable materials (i.e., rubbers capable of crosslinking) whichare modified in accordance with the present invention are theunsaturated hydrocarbon polymers exemplified by the diene polymers(which may be halogenated), such as polybutadiene, polychloroprene orpolyisoprene, especially polybutadiene or polyisoprene having a highcontent of cis-polymer or a low content of cis-polymer; copolymerrubbers such as butyl rubber (i.e., copolymers based on isomonoolefinssuch as isobutylene and a small amount [e.g. 0.25 to 10%]of a conjugateddiene such as isoprene), and even natural polymers such as balata, Hevearubber, and the like. Also, depolymerized rubber may be used. Otherunsaturated hydrocarbon polymers that may be mentioned are the rubberyinterpolymers of at least two alpha-monoolefins (e.g., ethylene,propylene, butene-1, hexene-1, 4-methylpentene-1, 5-methylhexene-1,4-ethylhexene-1, or similar olefins having the formula CH₂ = CHR, inwhich R is hydrogen or a hydrocarbon radical, particularly a saturatedalkyl hydrocarbon radical having from 1 to 8 carbon atoms) and at leastone copolymerizable diene such as dicyclopentadiene,methylcyclopentadiene dimer, 1,4-hexadiene, 11-ethyl-1, 11-tridecadiene,1,9-octadecadiene, 1,5-cyclooctadiene, methylene norbornene, ethylidenenorbornene or other suitable dienes (such rubbers are referred tohereinafter as "EPDM") such as are disclosed in British Pat. No. 880,904of Dunlop Rubber Co., Oct. 25, 1961, U.S. Pat. Nos. 2,933,480, Greshamand Hunt, Apr. 19, 1960, and 3,000,866, Tarney, Sept. 19, 1961 andBelgian Pat. Nos. 623,698 and 623,741 of Montecatini, Feb. 14, 1963;preferred are terpolymers of this kind containing from about 1 to about25% (more preferably about 2 to about 15%) by weight ofdicyclopentadiene or the like. In fact, the invention can be practicedwith rubbers prepared by methods other than solution polymerization, forexample by emulsion polymerization, e.g., emulsion polymerized dienehomopolymers or copolymers including butadiene-styrene copolymer orcopolymers with other copolymerizable monomers such as acrylonitrile,vinylpyridine, ethyl acrylate and the like.

The fiber-forming semi-crystalline thermoplastic resins which are addedto the rubbers noted above in accordance with the present invention,possess a melting point of about 250°F. or greater.

In order to be effective as a "no blow" additive the resin utilized inthe present invention is dispersed in the vulcanizable material in theform of particles having a cross sectional dimension (D) not greaterthan one-half micron and a length (L) to cross sectional dimension (D)ratio of 2 or greater. Unless the resin is dispersed in the vulcanizablematerial in the form of particles having the size limitations set forthabove, it is not possible to obtain free cured shaped articles which areof commercial quality.

The thermoplastic resin which is used in the present invention can varyso long as the rheological properties are such that the shear level ofmixing in the Banbury or on the mill is sufficient to bring thetemperature of the blend above the melting point of the resin. Also, itis desirable that the resin possess a softening temperature whichpermits cold remill of the blend wherein the active chemicals e.g.,curatives, accelerators, etc., are incorporated into the rubber-resinblend without softening the resin, and which permits a cure of therubber in a reasonable amount of time without completely melting theresin.

For the purpose of this specification "melting point of the resin" meansthe temperature at which the resin is completely melted. This pointvaries among the different resins included within the scope of thepresent invention, and can vary among the same resins because theseresins possess widely varying ranges of molecular weight distribution.In order to determine the temperature at which the resin undergoescomplete melting, a graph of the curve which represents shear stress asa function of temperature is obtained using a biconical rheometer.

Using the formula ##EQU1## where τ is shear stress, T is temperature, Tmis melting point of the resin and C is the slope of the curve, themelting point of the resin (Tm) is the temperature value (T) of theshear stress-temperature curve of any thermoplastic resin where theslope (C) becomes more than -0.02, and the value of shear stress (τ) isless than 5 psi, at a shear rate of 0.31 sec..sup.⁻¹. For example, theshear stress vs. temperature curve of polypropylene is shown in FIG. 1.The slope of the curve at the point where the resin is completely meltedis: ##EQU2## at a shear rate of 0.308 sec..sup.⁻¹.

Each rubber-resin blend used in the present invention possesses adifferent shear stress level at a constant shear stress It has beennoted that the shear stres value (τ) is less than 5 psi.

Using the conditions and values noted above, blends of varying amountsof polypropylene and the copolymer of ethylene (83% by wgt.) andmethacrylic acid (17% by wgt.) which has been 57% neutralized withsodium ions, (referred to as ionomer) were evaluated to determine themelting points. The blends were:

                   Slope C. Melting Point                                                        P.S.I./°F.                                                                      °F.                                            ______________________________________                                        75% Polypropylene (6723)                                                                       -0.02      338                                               25% Ionomer (1555)                                                            85% Polypropylene (6723)                                                                       -0.02      335                                               15% Ionomer (1555)                                                            95% Polypropylene (6723)                                                                       -0.02      332                                                5% Ionomer (1555)                                                            ______________________________________                                    

As the amount of ionomer present in the blend is decreased, the meltingof the resin blend decreases. This illustrates the application of theformula in determining the melting point of a typical resin system ofvarying compositions.

Some examples of useful resin polymers are:

A. Polyolefins having three (3) to six (6) carbon atoms in the repeatingunit such as polypropylene, poly (butene-1), poly (4-methylpentene-1),etc.

B. Polyamides which are present either as a homopolymer or a copolymerin which the amido group is an integral part of the polymer chain (i.e.,an intra-linear polyamide), or as a homopolymer or copolymer havingpendant groups containing or consisting of amido groups (i.e., anextra-linear polyamide).

Illustrative of intra-linear polyamides useful in this invention arehomopolyamides such as poly (hexamethylene adipamide) (Nylon 66), poly(hexamethylene sebacamide) (Nylon 610), polypyrrolidonone,polycaprolactam (Nylon 6), polyenantholactam and copolyamides such asZytel 61 (DuPont), an interpolymer of hexamethylene adipamide andhexamethylene sebacamide with caprolactam.

Examples of extra-linear polyamides are the poly (vinylpyrrolidonones)and polyacrylamides. Other examples of extra-linear polyamides arecopolymers of amido-group-containing vinyl monomers with other olefinicmonomers such as acrylic and methacrylic esters typified by ethylacrylate and methyl methacrylate, vinylaryl hydrocarbons typified bystyrene and vinyltoluenes, and butadiene-1,3. Still further examples aregraft copolymers of a previously formed linear high polymer, such aspolyethylene, polypropylene, polystyrene, and polybutadiene, with avinylpyrrolidonone or an acrylamide.

C. Also included are polyester resins which include condensationpolymers or dihydric alcohols with organo-dibasic acids, particularlydicarboxylic acids, and self-condensation polymers of omega-hydroxycarboxylic acids. It should be understood that the invention isapplicable to all film and fiber-forming polyesters, in which the esterlinkages are intralinear, including poly (alkylene alkanedioates),poly(cycloalkylenedimethylene alkanedioates), poly(alkylenearenedioates), poly(cycloalkylenedimethylene arenedioates), andanalogous materials. Examples of some of the above-named types ofpolyesters are poly(ethylene adipate), poly(1,4-cyclohexylenedimethyleneadipate), poly(ethylene terephithalate), poly(ethylene isophthalate),poly(co-ethylene terephthalate-isophthalate) andpoly(1,4-cyclohexylenedimethylene terephthalate).

D. Other useful polymers are the ionomers which are ionic copolymersprepared by neutralizing with metal ions at least 10% of the acid groupsof a copolymer of units derived from an α-olefin of the formula CHR=CH₂wherein R is H or an alkyl group having from 1 to 8 carbon atoms, andfrom 1.0 to 25 mole percent of units derived from an α,β-ethylenicallyunsaturated carboxylic acid. "Derived" means that the polymer units areobtained by copolymerization of the monomers named.

The ionomer is made by copolymerizing the α-olefin and carboxylic acid,described hereinbefore to form a copolymer in which the acid derivedunits are randomly distributed along the copolymer chain. The resultantacid copolymer is intimately contacted with a basic compound containingthe particular metal ion desired, to obtain the amount of neutralizationdesired. The preferred range of neutralization is from 10 to 100% by wt.of the acid groups present. "Neutralization" and variations of this workmean reacting the metal ion with the acid groups of the copolymer toobtain the ionic copolymer. Useful metal ions include those having avalence of 1 to 3 inclusive, and particularly those of Groups I (a andb) and II (a and b) and the transition elements of the Periodic Table.Because of the possibility of polyvalent metal ions forming basic salts,as much as 150% of the amount of such metal ion theoretically requiredfor neutralization can be used. The preferred mole percent of mono- ordicarboxylic acid derived units is from 3 to 15 mole percent. Examplesof olefins include ethylene, propylene, butene-1, and hexene-1. Examplesof the acids include acrylic, methacrylic acids and maleic and fumaricacids and monoalkyl esters and anhydrides thereof.

E. Acrylic polymers may also be used. This material is made from acopolymer composed of at least 85% acrylonitrile and 15% or less of suchcomonomers as vinyl acetate, acrylic esters and vinyl pyrrolidone. Otheruseful acrylic materials are the modacrylics containing 35-85%acrylonitrile and usually 20% or more vinyl chloride or vinylidenechloride; and the nytril composition, one example of which is a 1:1alternating copolymer of vinylidene cyanide and vinyl acetate. Apreferred acrylic resin is polyacrylonitrile.

Generally, between about 2 and 30 percent, preferably between 2 and 10percent (based on the total weight of composition) of the thermoplasticresin is added to the rubber in the form of particles having (D) notgreater than 1/2 micron and L/D of 2 or greater.

Depending upon the resin, in some instances the melt temperatures of themill are actually too high to properly melt the resin and allow for itsuniform incorporation into the rubber, and in such cases the masterbatchtechnique referred to previously can be utilized with rubber-resin ratioof 1:1-3:1.

The combination of polypropylene and between about 5 and 20% of anionomer as described (based upon the amount of polypropylene present inthe blend) provides an unusually useful additive to be blended into therubber. This combination results in easier processing of therubber-resin blend and improves the physical properties of thevulcanizate made from said blend.

U.S. Pat. No. 3,123,583, discloses a rubber-resin blend possessing from0.5 to 99.5 parts polyethylene resin per 100 parts of the blend. Theblending of rubber and resin is performed at a temperature of 270°F.(above the melting point of the resin) and subsequently the blend iscold milled at a temperature below 150°F., preferably 130°F. Thedistinction between the reference cited and the present invention isthat the reference discloses curing the rubber well above the meltingpoint of the resin, whereas in the present invention it is essentialthat the rubber be shaped and cured at a temperature below the meltingpoint of the thermoplastic resin additive. If the rubber-resin blend ofthe present invention is shaped and cured at a temperature above themelting point of the resin additive, the blowing phenomemon is noteliminated.

Initially, the rubber-resin blends of the present invention are blendedat a temperature above the melting point of the resin in any convenientmixing device which enables: (1) the attainment of a uniform blend, (2)the attainment of adequate dispersion of pigments, (i.e., avoidance oflumps and agglomerates of the pigments), and (3) production ofconsecutive batches which are uniform both in degree of dispersion andviscosity. Suitable mixers are roll mills or internal shear mixers suchas a Banbury, Intermix or Bolling mixer.

After blending, the rubber-resin blend is then cooled and curatives areadded to the blend. Any of the well known sulfur containing curativecompounds, as well as non-sulfur containing curative compounds includingoxidizing agents, (such as selenium, tellurium, organic peroxides, nitrocompounds, and the like) may be used. Preferred compounds to be used aresulfur and/or sulfur donating compounds such asN-t-butyl-2-benzothiazole sulfenamide, dipentamethylene thiuramhexasulfide and the organic peroxides such as dicumyl peroxide. Othersuitable compounds are dinitrosobenzene, quinone dioxime, anddimethylolphenols. All of these curatives are added in amounts ofbetween about 1 and 15 parts per 100 parts of rubber.

Other modifying or compounding ingredients may be incorporated into themixture of rubber and resin if desired. Thus, fillers such as carbonblack, clays, hydrate silica, whiting, or the like, may be present, aswell as pigments and dyes, mold release agents, softeners orplasticizers, tackifying agents, accelerators, etc.

The rubber-resin stock is formed into a shaped article after the twoblending steps and prior to vulcanization. The methods which can be usedto form the shaped article are extrusion, calendering, molding andlaminating operations or any desired combination thereof.

After the stock has been formed into a shaped article, it is ready for a"free cure".

The desired level of cure may range all the way from a slight precure(as disclosed, for example, in U.S. Pat. Nos. 2,702,286, 2,702,287 and2,756,801) to a complete vulcanization. The slight pre-cure may becarried out for various purposes, such as to improve processing, toimprove the dispersion of carbon black, silica and other fillers in therubber, to lower the hysteresis of such rubber-resin mixtures (whensubsequently vulcanized) to render the rubber more compatible with oilor with other rubbers, to provide a plastic puncture-sealing materialfor pneumatic tires or tubes, or to provide shorter curing time.

It will be understood that such slight pre-cure, is accomplished byheating the mixture of rubber-resin and curing agent, along with anyother desired ingredients, to a temperature sufficient to cause a slightvulcanization. Temperatures below the melting point of the resin must beused. Curing of the article may require only from 2 to 15 minutes if apre-cure treatment is used and up 8 hours without any pre-curetreatment, depending on such variables, as the type of treating mediumand the temperature of the treatment. Subsequently, a pre-cured articlemay be completely cured if desired.

It has been found to be very advantageous to preheat the stock orarticle by high frequency heating, e.g., micro-wave or dielectricheating, prior to the actual curing step since this type of preheatingenables shorter curing times and hence manufacturing costs to be reducedconsiderably. Dielectric heating is a method of inducing heat by a meansof an electromagnetic field of sufficient frequency and intensity tocause molecular stress and friction within the article being heated.Micro-wave heating is similar to dielectric heating but uses frequenciesin the 10⁹ to 10¹⁰ cps range. For simple shapes, the high frequencyheating permits fast and substantially even heating of the rubber stockor shaped article when it is placed in the electromagnetic highfrequency field.

Depending upon the temperature achieved in the article, the use of highfrequency preheating can virtually eliminate the induction timeassociated with the standard cure. Thus preheating to a highertemperature substantially reduces the time it takes to cure the article.(See FIG. 3 herein)

The stocks can be made more sensitive to high frequency heating byselectively utilizing fillers (e.g., special types of carbon black),rubbers, resins and cure systems to obtain the desired result.

One advantage obtained when preheating the rubber-resin stock of thepresent invention using a high frequency field is that the temperatureat which the rubber-resin stock blows is substantially raised ascompared with the blow temperature of an unmodified rubber, i.e., onewhich does not contain the thermoplastic resins described herein.

Through the use of the substantially complete free cure of the rubberaccording to the present invention strong, elastic, and resilient curedarticles such as curing bags, steam hose, conveyor belts, pneumatictires, rubber mountings, fuel cells, protective clothing, and similararticles may be obtained. The vulcanization step consists of heating thestock or shaped article to the proper cure temperature for the requiredlength of time. The time required to substantially complete the curewill vary widely in practice depending on such variables as the quantityof the curing agents employed, the temperature at which the process iscarried out, the size of the article being cured, the type of apparatusemployed, the extent of preheating, etc. In general, it may be statedthat satisfactory cures may be obtained within curing times rangingbetween about 2 minutes to 8 hours. It will be understood that the timerequired will in general be inversely related to the quantity of thevulcanizing agent contained in the mixture, and will also be inverselyrelated to the temperature existing during the cure. Any of the standardmethods of vulcanization may be used such as mold curing, injectioncuring, steam curing, hydraulic curing, air curing, etc. Combinations ofthe aforesaid methods may also be utilized. For example, the stock maybe heated and/or partially free cured in air and completed in the mold,or partially cured in the mold and free cured in air with or withoutadditional heat to complete the cure. In standard molding practice,curing pressures at or above the water vapor pressure for the givencuring temperature are used. As noted previously, the present inventionallows a marked decrease in the required curing pressure at curingtemperatures above 220°F. When fabricating an article having componentparts using a calendering, molding, extrusion operation, etc., it isnecessary to achieve intimate contact between said parts by applyingpressure thereto. This application of pressure is known asconsolidation.

The following examples, in which all parts and percentages are byweight, will serve to illustrate the practice of the invention in moredetail.

EXAMPLE I

Two masterbatch compositions described in Tables 1 and 2 were mixed(separately) in a Banbury mixer.

    ______________________________________                                        Table 1           Table 2                                                     Stock 1           Stock 2                                                     ______________________________________                                        Compound    Parts     Compound      Parts                                     ______________________________________                                        Natural Rubber                                                                            22        Natural Rubber                                                                              22                                        Cis-polybutadiene                                                                         28        Cis-polybutadiene                                                                           28                                        poly(butadiene-co-    poly(butadiene-co-                                       styrene).sup.1                                                                           75         styrene).sup.1                                                                             75                                        Carbon Black                                                                              57.5      Carbon Black  57.5                                      Stearic Acid                                                                              1         Stearic Acid  1                                         Zinc Oxide  5         Zinc Oxide    5                                         Activators  4         Activators    4                                         Pine Tar    7         Pine Tar      7                                         Plasticizers                                                                              2.9       Plasticizers  2.9                                                             Polypropylene 75                                        Total       202.4                   277.4                                     ______________________________________                                         .sup.1 Contains 22-24% by wt. bound styrene.                             

The ingredients of Stock 1 were added to the Banbury and mixed until thetemperature of the batch reached 285°F.

The polypropylene component of Stock 2 was added to the Banbury whichwas preheated by circulating steam through the rotors and jacket of themixer. The polypropylene was subjected to shear for 2 minutes, whereuponthe Banbury was stopped and the rest of the ingredients were added andthe batch was blended until the temperature of the stock reached380°-390°F.

At the end of the initial mixing cycle each stock was allowed to cool.

Stocks 1 and 2 were then blended together in various amounts on a mixingmill at 340°F, in the proportion shown in Tables 3-6.

    __________________________________________________________________________    Table 3            Table 4                                                    Stock 3            Stock 4                                                    __________________________________________________________________________    Compound 3   Parts Compound 4   Parts                                         __________________________________________________________________________    Stock 1      202.4 Stock 1      188.9                                         Hexa-5-Methanol    Stock 2      18.5                                           (3,7)dioxibicyclo                                                             (3,3,0) octane*                                                                           1.25  Hexa-5-Methanol                                                                (3,7)dioxibicyclo                                         N-tert butyl-2-benzo-                                                                             (3,3,0) octane*                                                                           1.25                                           thiazole sulfena-                                                             mide*       0.90  N-tert butyl-2-benzo-                                                          thiazole sulfena-                                         Accelerator* 0.25   mide*       0.90                                          Sulfur*      3.25  Accelerator* 0.25                                                             Sulfur*      3.25                                          Total        208.05                                                                              Total        213.05                                        Table 5            Table 6                                                    Stock 5            Stock 6                                                    __________________________________________________________________________    Compound     Parts Compound     Parts                                         __________________________________________________________________________    Stock 1      175.4 Stock 1      161.9                                         Stock 2      37.0  Stock 2      55.5                                          Hexa-5-Methanol    Hexa-5-Methanol                                             (3,7)dioxibicyclo  (3,7)dioxibicyclo                                          (3,3,0) octane*                                                                           1.25   (3,3,0) octane*                                                                           1.25                                          N-tert butyl-2-benzo-                                                                            N-tert butyl-2-benzo-                                       thiazole sulfena-  thiazole sulfena-                                          mide*       0.90    mide*      0.90                                          Accelerator* 0.25  Accelerator* 0.25                                          Sulfur*      3.25  Sulfur*      3.25                                          Total        218.05                                                                              Total        223.05                                        __________________________________________________________________________      *These compounds were added to the stock after blending and cooling of       the other materials listed in the tables.                                

In each case, the rubber was milled long enough to insure uniformdistribution of materials throughout the batch. The blended stock werethen removed from the mill and allowed to cool.

Each of the blended stocks was placed separately on a cold mill whichwas at no time permitted to exceed a temperature of 170°F. and thesulfur and accelerators noted in Tables 3-6 were added. The stocks wereeach cut back and forth about six times to insure thorough blending,sheeted off the mill, cooled and then cured after shaping andconsolidation.

The cured stocks (carcass stocks) were subjected to testingconventionally as shown to determine the effect of the polypropylene onnormal stock properties. The results are given in Table 7. The tensilestrength and elongation were run on a Scott machine, and the modulus wasrun on an autographic stress-strain machine.

                                      Table 7                                     __________________________________________________________________________    Test          Stock 3                                                                              Stock 4                                                                              Stock 5                                                                              Stock 6                                    __________________________________________________________________________    Polypropylene %                                                                             0      2.4    4.8    7.2                                        ML-4 212°F.                                                                          47     46     51     57                                         Mooney Scorch (MS)                                                            MS, Minimum   20.0   18.0   16.0   18.0                                       3 Pt. rise, Mins.                                                                           28.6   30.5   31.8   32.0                                       23 Pt. rise, Mins.                                                                          31.6   33.8   35.6   35.5                                        Δ MS, Mins.                                                                          3.0    3.3    3.8    3.5                                        Cure, Mins, at 315°F.                                                                20     20     20     20                                         Autographic:                                                                   S-200 Psi    720    830    915    1050                                        S-300        1280   1420   1500   1630                                       Tensile Psi   2050   1620   1875   2000                                       E.sub.b %     440    335    370    370                                        Durometer     57     59     61     66                                         Tear 250°F., ppli                                                                    73     68     76     104                                        Scott:                                                                         Tensile, RT  2320   2480   2430   2450                                        250°F.                                                                              800    963    963    1080                                        E.sub.b % RT 430    410    390    350                                         250°F.                                                                              240    290    280    300                                        Goodrich Flex 212°F.                                                   Static defl., %                                                                             15.0   15.0   12.5   11.6                                       15 min. Temp. rise                                                                          28     28     31     35                                         Dynamic drift %                                                                             0.3    0.8    1.4    2.0                                        Perm set %    3.0    3.4    3.4    4.0                                        Torsional Hyst. R.T.                                                                        .195   .205   .209   .233                                        280°F.                                                                              .088   .083   .091   .099                                       Bashore Rbd, R.T.                                                                           48     47     46     41                                         Flexcracking, kc.                                                                           183.6  495.9  194.4  300.4                                      Air permeability                                                                       86°F.                                                                       3.77   3.18   3.25   2.74                                       × 10.sup.-.sup.3                                                                 140°F.                                                                      11.9   10.1   10.5   9.1                                        __________________________________________________________________________

This example shows that as the loading proportion of polypropylene isincreased from zero to 7.2%, the viscosity (ML-4) increases from 47 to57. The stock becomes a little less "scorchy" as shown by the increasein time for a 23 point rise from 31.6 to 35.5 minutes. When cured 20minutes at 315°F., the stiffness of the compound increases with loadingas shown by the increase in S-200 and S-300 and by the increase indurometer. The room temperature tensile strength is not greatly affectedbut the tensile at 250°F, increases some with loading. Energy loss onflexing increases with loading as shown by Goodrich Flexometertemperature rise, torsional hysteresis, and Bashore rebound. The effectof loading on flexcracking is mixed, while there is a slight reductionin air permeability.

EXAMPLE 2

The two masterbatch compositions described in Table 8 were mixed(separately) in a Banbury mixer.

                  Table 8                                                         ______________________________________                                        Stock 7           Stock 8                                                     Compound    Parts     Compound      Parts                                     ______________________________________                                        Poly(butadiene-co-    Poly(butadiene-co-                                       styrene)1500.sup.1                                                                       13         styrene)1500.sup.1                                                                         13                                        Poly(butadiene-co-    Poly(butadiene-co-                                       styrene)1712.sup.1                                                                       85         styrene)1712.sup.1                                                                         85                                        Cis-polybutadiene                                                                         25        Cis-polybutadiene                                                                           25                                        Reclaim 655 65        Reclaim 655   65                                        Carbon Black                                                                              60        Carbon Black  60                                        Stearic Acid                                                                              1.25      Stearic Acid  1.25                                      Zinc Oxide  3.50      Zinc Oxide    3.50                                      ENSO 50     4.20      ENSO 50       4.20                                      Antiozonant 1.50      Antiozonant   1.50                                                            Polypropylene 75                                        Total       258.45    Total         333.45                                    ______________________________________                                         .sup.1 Contains 22-24% by wt. bound styrene.                             

The ingredients of Stock 7 were added to the Banbury and mixed until thetemperature of the batch reached 280°F.

The polypropylene component of Stock 8 was added to the Banbury whichwas preheated by circulating steam through the rotors and jacket of themixer. The polypropylene was subjected to shear for two minutes,whereupon the Banbury was stopped and the rest of the ingredients wereadded and the batch was blended until the temperature of the stockreached 360°-390°F.

At the end of the mixing cycle of Stocks 7 and 8 both were allowed tocool.

Stocks 7 and 8 were then blended together in various amounts on a mixingmill at 340°F. in the proportions shown in Tables 9-12.

    __________________________________________________________________________    Table 9            Table 10                                                   Stock 9            Stock 10                                                   __________________________________________________________________________    Compound     Parts Compound     Parts                                         __________________________________________________________________________    Stock 7      258.45                                                                              Stock 7      240.95                                        N-tert-butyl-2-benzo-                                                                            Stock 8      22.50                                          thiazole-sulfen-                                                              amide*      0.70  N-tert-butyl-2-benzo-                                                          thiazole-sulfen-                                          Accelerator* 0.10   amide*      0.70                                          Sulfur*      3.00  Accelerator* 0.10                                                             Sulfur*      3.00                                          Total        262.25                                                                              Total        267.25                                        __________________________________________________________________________    Table 11           Table 11                                                   Stock 11           Stock 12                                                   __________________________________________________________________________    Compound     Parts Compound     Parts                                         __________________________________________________________________________    Stock 7      223.45                                                                              Stock 7      205.95                                        Stock 8      45.0  Stock 8      67.5                                          N-tert-butyl-2-benzo-                                                                            N-tert-butyl-2-benzo-                                       thiazole-sulfen-   thiazole-sulfen-                                           amide*      0.70   amide*      0.70                                          Accelerator* 0.10  Accelerator* 0.10                                          Sulfur*      3.0   Sulfur*      3.0                                           Total        272.25                                                                              Total        277.25                                        __________________________________________________________________________     *These compounds were added to the stock after blending and cooling of th     other materials in the table.                                            

The rubber was milled long enough to insure uniform distribution ofmaterials throughout the batch whereupon each of the blended stocks wasremoved from the mill and allowed to cool.

Each of the blends was placed separately on a cold mill which was at notime permitted to exceed 170°F. and the sulfur and accelerators noted inTables 9-12 were added. The stocks were each cut back and forth aboutsix times to insure thorough blending, sheeted off the mill, cooled andthen cured after shaping and consolidation.

The cured stocks (sidewall stocks) were subjected to testingconventionally as shown to determine the effect of polypropylene on thenormal stock properties. The results are given in Table 13. The tensilestrength and elongation were run on a Scott machine, and the modulus wasrun on an autographic stress-strain machine.

                                      Table 13                                    __________________________________________________________________________    Test          Stock 9                                                                              Stock 10                                                                             Stock 11                                                                             Stock 12                                   __________________________________________________________________________    Polypropylene %                                                                             0      1.9    3.8    5.7                                        ML-4 212°F.                                                                          59     57     65     73                                         Mooney Scorch (MS)                                                             270°F.                                                                              23.9   23.6   26.2   29.2                                       3 Pt. rise, Mins.                                                                           20.6   20.8   22.1   21.1                                       23 Pt. Rise, Mins.                                                                          25.2   26.7   27.1   25.4                                       Δ MS, Mins.                                                                           4.6    5.9    5.0    4.3                                        Cure, Mins., at 315°F.                                                               20     20     20     20                                         Autographic:                                                                   S-200 Psi    510    590    650    800                                         S-300        900    970    1040   1200                                        Tensile Psi  1650   1580   1620   1470                                        E.sub.b %    495    465    460    375                                         Durometer    51     54     56     61                                          Tear 250°F., ppli                                                                   78     88     66     67                                         Scott:                                                                         Tensile, RT  1660   1840   1850   1860                                        250°F.                                                                              633    643    683    723                                         E.sub.b % RT 420    450    430    390                                         250°F.                                                                              280    290    280    280                                        Goodrich Flex 212°F.                                                   Static defl., %                                                                             19.8   19.4   19.8   19.8                                       15 min. Temp. rise                                                                          47     50     51     57                                         Dynamic drift %                                                                             4.3    5.6    7.1    10.6                                       Perm set %    10.0   10.8   12.2   13.8                                       Torsional Hyst. R.T.                                                                        .282   .293   .331   .346                                        280°F.                                                                              .112   .152   .119   .129                                       Bashore Rbd, R.T.                                                                           43     42     40     37                                         Flexcracking, kc.                                                                           551    775    523    360                                        Air Permeability                                                              × 10.sup.-.sup.3) 86°F.                                                        2.38   2.02   2.13   1.85                                       140°F. 9.24   8.20   8.49   7.49                                       __________________________________________________________________________

The results, when examined as a function of loading of polypropylene,show much the same trends as disclosed by Table 7, namely an increase instiffness, an increase in tensile, and an increase in energy loss onflexing. Air permeability is again reduced.

EXAMPLE 3

The two masterbatch compositions described in Table 14 were mixed(separately) in a Banbury mixer.

                  Table 14                                                        ______________________________________                                        Stock 13          Stock 14                                                    Compound    Parts     Compound      Parts                                     ______________________________________                                        Poly(butadiene-co-    Poly(butadiene-co-                                       styrene)8202.sup.1                                                                       105        styrene)8202.sup.1                                                                         105                                       Cis-polybutadiene                                                                         30        Cis-polybutadiene                                                                           30                                        Carbon Black                                                                              70        Carbon Black  70                                        Zinc Oxide  3         Zinc Oxide    3                                         Stearic Acid                                                                              1.0       Stearic Acid  1.0                                       ENSO 50     2.0       ENSO 50       2.0                                       Antiozonant 0.5       Antiozonant   0.5                                       Sundex 790  7         Sundex 790    7                                                               Polypropylene 75                                        Total       218.5     Total         293.5                                     ______________________________________                                         .sup.1 Contains 22-24% by wt. bound styrene.                             

The ingredients of Stock 13 were added to the Banbury and mixed untilthe temperature of the batch reached 300°-310°F.

The polypropylene component of Stock 14 was added to the Banbury whichwas preheated by circulating steam through the rotors and jacket of themixer. The polypropylene was subjected to shear for 2 minutes, whereuponmixing was stopped and the rest of the ingredients were added and theresultant batch was blended until the temperature of the stock reached360°-390°F.

At the end of the mixing cycle, Stocks 13 and 14 were allowed to cool.

Stocks 13 and 14 were then blended together in various amounts on amixing mill at 300°F. in the proportions shown in Tables 15-18.

    ______________________________________                                        Table 15               Table 16                                               Stock 15               Stock 16                                               ______________________________________                                        Compound   Parts           Compound   Parts                                   ______________________________________                                        Stock 13   218.5           Stock 13   203.9                                   Accelerator*                                                                             1.3             Stock 14   19.6                                    Sulfur*    1.75            Accelerator*                                                                             1.3                                                                Sulfur*    3.25                                    Total      221.35          Total      226.55                                  ______________________________________                                        Table 17               Table 18                                               Stock 17               Stock 18                                               ______________________________________                                        Compound   Parts           Compound   Parts                                   ______________________________________                                        Stock 13   189.4           Stock 13   174.8                                   Stock 14   39.1            Stock 14   58.7                                    Accelerator*                                                                             1.3             Accelerator*                                       Sulfur*    1.75            Sulfur*    1.3                                                                           1.75                                    Total      231.55          Total      236.55                                  ______________________________________                                         *These compounds were added to the stock after blending and cooling of th     other materials in the table.                                            

The rubber was milled long enough to insure uniform distribution ofmaterials throughout the batch whereupon each of the blended stocks wasremoved from the mill and allowed to cool.

The blended stocks were placed separately on a mill maintained below170°F. and the sulfur and accelerators noted in Tables 15-18 were added.A separate batch of stock 14 used in stock 18B was prepared usingpolypropylene in fine powder form instead of the pellet form used instocks 1-18A. Every precaution was taken to keep this well below thesoftening temperature of polypropylene at all stages of processing:masterbatching, blending and accelerator addition. The stocks were eachcut back and forth about six times to insure thorough blending. A shapedand consolidated article was formed from the stock which was then cured.The cured stocks (tread stocks) were subjected to testing conventionallyas shown to determine the effect of polypropylene on the normal stockproperties. The results are given in Table 19. The tensile strength andelongation were run on a Scott machine, and the modulus was run on anautographic stress-strain machine.

                                      Table 19                                    __________________________________________________________________________    Test          Stock 15                                                                             Stock 16                                                                             Stock 17                                                                             Stock 18                                   __________________________________________________________________________                                       A.sup.1                                                                              B.sup.2                             Polypropylene %                                                                             0      2.1    4.2    6.3    6.3                                 ML-4 212°F.                                                                          62     67     77     104    --                                  Mooney Scorch (MS)                                                             270°F.                                                                 MS, Minimum  25.7   27.9   29.8   35.6   --                                    3 Pt. rise, Mins.                                                                         19.9   19.1   18.5   19.8   --                                   23 Pt. rise, Mins.                                                                         24.2   22.8   22.6   23.0   --                                   MS, Mins.    4.3    3.7    4.1    3.2    --                                  Cure, Mins. at 315°F                                                                 15     15     15     15     15                                  Autographic:                                                                   S-200 Psi    480    770    920    1090   480                                  S-300        950    1230   1400   1560   930                                  Tensile Psi  1810   1730   1750   1780   1540                                 E.sub.b %    475    410    375    350    435                                 Durometer                                                                     Tear 250°F., ppli                                                                    116    199    194    205    78                                  Scott:                                                                         Tensile, RT  2080   2170   1960   2160   1780                                 250°F.                                                                              877    1030   993    1020   647                                  E.sub.b %    420    390    320    330    420                                  250°F.                                                                              310    300    300    300    270                                 Goodrich Flex 212°F.                                                   Static defl., %                                                                             16.1   16.7   16.2   13.5   --                                  15 min. temp. rise                                                                          48     58     60     63     --                                  Dynamic drift %                                                                             3.0    5.0    9.0    9.4    --                                  Perm set %    8.0    9.5    11.8   10.3   --                                  Torsional Hyst, R.T.                                                                        0.402  0.472  0.473  0.483  0.425                                280°F.                                                                              0.149  0.169  0.199  0.195  0.151                               Bashore Rbd, R.T.                                                                           36     35     32     31     --                                  Flexcracking  858    387    226    93     --                                  Air Permeability 86°F.                                                               3.04   2.54   2.69   2.38   --                                   (× 10-3) 140°F.                                                               9.90   8.54   9.07   8.29   --                                  __________________________________________________________________________     A.sup.1 -represents a blend wherein polypropylene was added in the same       pellet form used in stocks 1 through 18A.                                     B.sup.2 -represents a blend wherein polypropylene powder was cold milled      into the composition.                                                    

The results considered as a function of polypropylene loading are ingeneral a repetition of the trends found in Tables 7 and 13, anexception being the great improvement in hot tear strength as theloading increases.

EXAMPLE 4

This example discloses the preparation of blends of various rubbers andpolypropylene resin.

The compositions set forth in Tables 20-24 were blended in a Banburymixer.

                  Table 20                                                        ______________________________________                                        Stock 19 (Footwear composition)                                               Compound                  Parts                                               ______________________________________                                        Poly (butadiene-co-styrene) 8140.sup.1                                                                  100.00                                              Hydrated silica 215       34.14                                               Chlorinated Paraffin Oil  43.90                                               R-202                     8.30                                                Polyethylene glycol 4000  4.21                                                Hydrated sodium silica aluminate                                                                        3.38                                                S.W. Crystals             0.27                                                Hydrocarbons (65% straight chain and                                          35% branched chains)      0.31                                                Zinc Oxide                1.01                                                Total                     194.52                                              ______________________________________                                         .sup.1 Contains 22% by weight bound styrene.                             

                  Table 21                                                        ______________________________________                                        Stock 20 (Red Sheet composition)                                              Compound                  Parts                                               ______________________________________                                        Poly(butadiene-co-styrene) 1713.sup.1                                                                   21.89                                               Zinc Oxide                0.66                                                Magnesium carbonate       1.46                                                Clay                      33.56                                               Natural calcium carbonate 35.02                                               Red Oxide                 1.46                                                Paraffin petroleum oil    1.46                                                Unsaturated hydrocarbon polymers                                                                        1.17                                                Plasticizer-9             0.58                                                Tycol albawax 23          0.22                                                Polyethylene glycols 4000 0.15                                                Stearic acid              0.22                                                Alkylated bis phenol      0.22                                                Polyethylene AC-617       0.73                                                Total                     98.80                                               ______________________________________                                         .sup.1 Contains 22% by wt. bound styrene.                                

                  Table 22                                                        ______________________________________                                        Stock 21 (EPDM)                                                               Compound                  Parts                                               ______________________________________                                        Ethylene-propylene-diene Terpolymer 502                                                                 100.0                                               Carbon black HA2          50.00                                               Naphthenic oil            15.00                                               Zinc Oxide                5.00                                                Stearic acid              1.00                                                Total                     171.00                                              ______________________________________                                    

                  Table 23                                                        ______________________________________                                        Stock 22 (Neoprene)                                                           Compound                  Parts                                               ______________________________________                                        Polychloroprene (WHV)     6.40                                                Poly(butadiene-co-styrene) 1808.sup.1                                                                   22.86                                               Zinc Oxide                1.01                                                Magnesium oxide           0.37                                                Chloroprene M-40          9.14                                                Natural calcium carbonate 33.83                                               Carbon black SRF          9.14                                                Plasticizer RT-3          0.29                                                Vulcanized vegetable oil  4.57                                                Aromatic oil-silicate blend                                                                             9.14                                                Plasticizer ZO-9          0.73                                                Tycol Albawax 23          0.24                                                Stearic Acid              0.16                                                Polyethylene AC-617       1.10                                                Total                     98.98                                               ______________________________________                                         .sup.1 Contains 22-24% by wt. bound styrene.                             

                  Table 24                                                        ______________________________________                                        Stock 23 (Butyl Rubber)                                                       Compound                 Parts                                                ______________________________________                                        Poly(Isobutylene-co-Isoprene).sup.1                                                                    56.82                                                Magnesium oxide          0.57                                                 Zinc oxide               1.70                                                 Carbon black FEA         17.05                                                Carbon black HAF         17.05                                                Paraffinic oil           2.84                                                 Petrolatum-silicate blend                                                                              0.57                                                 Stearic acid             0.57                                                 Paraffin wax             0.57                                                 Total                    98.31                                                ______________________________________                                         .sup.1 (1.1-1.7 mole % isoprene)                                         

                                      Table 25                                    __________________________________________________________________________               Stock 24                                                                            Stock 25                                                                            Stock 26                                                                            Stock 27                                                                            Stock 28                                   __________________________________________________________________________    Polypropylene                                                                            100   100   100    80   100                                        Ionomer (Surlyn A)            20                                              Stock 19   300                                                                Stock 20         300                                                          Stock 21               300                                                    Stock 22                     300                                              Stock 23                           300                                         Total in Parts                                                                          400   400   400   400   400                                        __________________________________________________________________________

Stocks 19-23 were prepared separately by adding the ingredients listedinto a Banbury internal shear mixer and mixing until the temperature ofthe batch was approximately 250°F.

A masterbatch blend was then prepared by adding the polypropylenecomponent of Stocks 24 through 28 (See Table 25 above) in each instanceinitially to a Banbury mixer which was preheated by circulating steamthrough rotors and jacket of the mixer. The polypropylene was subjecedto shear for two minutes whereupon, the Banbury was stopped and theother components listed were added and the batches were each blendeduntil the temperatures of the stock in each case reached about 380°F.

Each masterbatch of stocks 24-28 were then separately blended with theappropriate stock 19-23 (as listed in Tables 16-30) on a mixing mill at330°F. to obtain a composition having between 2 and 25% polypropylenebased on total weight.

Accelerators and sulfur were added to the appropriate stocks at 150°F.in a Banbury to form the compositions shown in Tables 26-31.

                  Table 26                                                        ______________________________________                                        Stocks 29 and 30                                                              Compound               Parts                                                                       Stock 29                                                                             Stock 30                                          ______________________________________                                        Stock 19               194.52   162.10                                        Stock 24                        32.42                                         N-t-butyl-2-benzothiazole sulfenamide                                                                1.06     1.06                                          Di-penta-methylene-thiuramhexasulfide                                                                0.33     0.33                                          Zinc dimethyl dithiocarbamate                                                                        1.13     1.13                                          Sulfur                 3.58     3.58                                          Total                  200.62   200.62                                        ______________________________________                                    

                  Table 27                                                        ______________________________________                                        Stocks 31 and 32                                                              Compound            Parts                                                                       Stock 31 Stock 32                                           ______________________________________                                        Stock 20            98.80      69.04                                          Stock 25                       19.76                                          Di-ortho-tolylguanidine                                                                           0.10       0.10                                           N-cyclohexyl-2-benzothiazole                                                  sulfenamide         0.32       0.32                                           Sulfur              0.80       0.80                                           Total               100.02     100.02                                         ______________________________________                                    

                  Table 28                                                        ______________________________________                                        Stocks 33 and 34                                                              Compound            Parts                                                                       Stock 33 Stock 34                                           ______________________________________                                        Stock 21            171.00     136.60                                         Stock 26            --         34.20                                          Tetramethylthiuram monosulfide                                                                    0.50       0.50                                           2-Mercaptobenzothiazole                                                                           1.50       1.50                                           Sulfur              1.50       1.50                                           Total               174.50     174.30                                         ______________________________________                                    

                  Table 29                                                        ______________________________________                                        Stocks 35 and 36                                                              Compound            Parts                                                                       Stock 35 Stock 36                                           ______________________________________                                        Stock 22            98.98      79.18                                          Stock 27            --         19.80                                          Tetramethylthiuram monosulfide                                                                    .22        0.22                                           Di-orthotolylguanidine                                                                            .20        0.20                                           Sulfur              .59        0.59                                           Total               99.99      99.99                                          ______________________________________                                    

                  Table 30                                                        ______________________________________                                        Stocks 37 and 38                                                              Compound            Parts                                                                       Stock 37 Stock 38                                           ______________________________________                                        Stock 23            98.31      68.65                                          Stock 28                       19.66                                          Benzothiazyl disulfide                                                                            1.14       1.14                                           Tetramethylthiuram disulfide                                                                      .57        .57                                            Total               100.02     100.02                                         ______________________________________                                    

Various amounts of Surlyn A (1555) (an ionomer consisting of ethyleneand the partial sodium salt of methacrylic acid) were blended with theblend of stocks 19 and 24 on a mixing mill at 300°F. to form thecompositions shown in Table 31. Then the accelerators and sulfur wereadded to these mixed compounds at 150°F. to form the compositions shownin Tables 26-31.

In each case the compound is milled long enough to insure uniformdistribution of materials throughout the batch. The blends, formingstocks 29-43, are then removed from the mill and allowed to cool.

                                      Table 31                                    __________________________________________________________________________               Stock 39                                                                            Stock 40                                                                            Stock 41                                                                            Stock 42                                                                            Stock 43                                   __________________________________________________________________________    Stock 19   162.10                                                                              162.10                                                                              162.10                                                                              162.10                                                                              162.10                                     Stock 24   32.42 32.42 32.42 32.42 32.42                                      Surlyn A (1555)                                                                          2.00  4.00  6.00  8.00  10.00                                      N-t-Butyl-2-benzo-                                                            thiazole sulfinamide                                                                     1.06  1.06  1.06  1.06  1.06                                       D-pentamethylene                                                              thiuramhexasulfide                                                                       0.33  0.33  0.33  0.33  0.33                                       Zinc dimethyldi-                                                              chlorocarbamate                                                                          1.33  1.33  1.33  1.33  1.33                                       Sulfur     3.58  3.58  3.58  3.58  3.58                                       Total      202.82                                                                              204.82                                                                              206.82                                                                              208.82                                                                              210.82                                     __________________________________________________________________________

EXAMPLE 5

Each stock set forth in Table 32 was pressed at 212°F. into a discmeasuring 2 inches in diameter by 1/4 inch in thickness. The densitiesof the uncured compounds and the compounds cured in a standard ovenwithout pressure were measured precisely, in order to determine thedegree of blow. The compounds were cured in the oven using a standardcure cycle at 310°F.

The relative values of the increase or the decrease in density arecomputed on the basis of the density of the uncured stocks. A compoundwhich has a 3 percent change or less in density is considered to be a noblow compound. The results are given in Table 32.

                                      TABLE 32                                    __________________________________________________________________________    RESULTS OF DENSITY MEASUREMENT                                                                 Density                                                                              Density                                                                (ρ.sub.a g/cc)                                                                   (ρ.sub.b g/cc)                                                     of Uncured                                                                           of Cured                                                                             ρ.sub.b - ρ.sub.a                                                         × 100 (%)                            Stock   Blend    Composition                                                                          Composition                                                                          ρ.sub.a                                    __________________________________________________________________________    Stock 3          1.1219 1.0659 -4.99                                          Stock 4                                                                             (Carcass + PP.sup.1)                                                                     1.1283 1.0967 -2.87                                          Stock 5                                                                             (Carcass + PP)                                                                           1.1292 1.0991 -2.66                                          Stock 6                                                                             (Carcass + PP)                                                                           1.1219 1.1135 -0.75                                          Stock 9                                                                             (Sidewall) 1.1422 1.0281 -9.98                                          Stock 11                                                                            (Sidewall + pp)                                                                          1.1352 1.0985 -3.00                                          Stock 12                                                                            (Sidewall + PP)                                                                          1.1226 1.1041 -1.65                                          Stock 15                                                                            (Tread)    1.1170 1.0710 -4.13                                          Stock 17                                                                            (Tread + PP)                                                                             1.1340 1.1290 -0.37                                          Stock 18                                                                            (Tread + PP)                                                                             1.1030 1.1350 +2.90                                          Stock 29                                                                            (Footwear) 1.0755 0.7793 -27.55                                         Stock 30                                                                            (Footwear + PP)                                                                          1.0675 1.0439 -2.21                                          Stock 31                                                                            (Red Sheet)                                                                              1.6480 1.4831 -10.00                                         Stock 32                                                                            (Red Sheet +  PP +                                                                       1.6489 1.5835 -3.00                                                 SA)                                                                    Stock 33                                                                            (EPDM)     1.0561 0.7299 -30.88                                         Stock 34                                                                            (EPDM + PP)                                                                              1.0376 1.0220 -1.50                                          Stock 35                                                                            (Neoprene) 1.3374 1.1304 -15.50                                         Stock 36                                                                            (Neoprene + PP +                                                               SA)       1.4208 1.4118 -0.63                                          Stock 37                                                                            (Butyl)    1.1178 0.8574 -23.34                                         Stock 38                                                                            (Butyl + PP)                                                                             1.1033 1.0748 -2.58                                          Stock 39                                                                            (Footwear + PP +                                                               SA)       1.0721 1.0727 +0.06                                          Stock 40                                                                            (Footwear + PP +                                                               SA)       1.0692 1.0675 -0.17                                          Stock 41                                                                            (Footwear + PP +                                                               SA)       1.0674 1.0699 +0.23                                          Stock 42                                                                            (Footwear + PP +                                                               SA)       1.0673 1.0691 +0.17                                          Stock 43                                                                            (Footwear + PP +                                                               SA)       1.0650 1.0695 +0.42                                          __________________________________________________________________________     PP represents polypropylene.                                                  *SA represents ionomer of ethylene and half salt of methacrylic acid.         NOTE:                                                                         A (-) denotes that density of cured article decreased by the amount given     and a (+) denotes that density of the cured article increased by the          amount given.                                                            

This Example shows that rubber compounds prepared as disclosed hereinand which have been modified in accordance with the present inventionfree cure in an oven without pressure. The problem of blowing isvirtually eliminated.

EXAMPLE 6

The tensile strength of each of the stocks 29-32 indicated in Table 33was measured to determine the extent of blowing. Each of the stocks asprepared herein were cured at 310°F. in a hot air oven using a pressuresystem (i.e., a standard press cure in a platen) for some of thesamples, and using a free cure system without pressure for the othersamples.) The tensile strengths and elongations of the stocks curedusing both systems were run on a Scott machine. The tensile strength ofthe stocks which were cured without pressure decreased sharply, whilethe change in tensile strength of no blow stock is insignificant. Theresults are given in Table 33.

                  Table 33                                                        ______________________________________                                        Tensile Strength and Elongation                                               1.  Pressure Cure                                                                            Tensile Strength                                                                          Elongation                                         ______________________________________                                                         (Psi)                                                        Stock 29 (Footwear)                                                                            650           360                                            Stock 30 (Footwear + PP)                                                                       887           300                                            Stock 31 (Red sheet)                                                                           493           260                                            Stock 32 (Red sheet + PP)                                                                      680           110                                            2.  Oven Cure Without Pressure                                                                 Tensile Strength                                                                            Elongation                                     ______________________________________                                                         (Psi)                                                        Stock 29 (Footwear)                                                                            570           360                                            Stock 30 (Footwear + PP)                                                                       810           280                                            Stock 31 (Red sheet)                                                                           197           250                                            Stock 32 (Red sheet + PP)                                                                      577           100                                            ______________________________________                                         PP represents polypropylene                                              

EXAMPLE 7

The blowing temperature of a rubber compound blend of rubber plus resincan be determined by microwave cure. The small disc samples were placedin a microwave oven having a nominal power output of 1 kilowatt R.F.energy at 2,450 megacycles. The resonant cavity is 12 × 12 × 6 inches.Energy is supplied until the stocks blow and burn. The temperaturesafter blowing and burning have been measured with the sensitivethermocouples. The results of curing stocks 15, 18, 37 and 38 in themicrowave oven are shown in Table 34.

                  Table 34                                                        ______________________________________                                        Results of Microwave Cure                                                                    Blow Temp.                                                                              Burn Temp.                                                          °F.                                                                              °F.                                           ______________________________________                                        Stock 15 (Tread) 290         420                                              Stock 18 (Tread + PP)                                                                          380         500                                              Stock 37 (Butyl) 270         370                                              Stock 38 (Butyl + PP)                                                                          364         450                                              ______________________________________                                         PP represents polypropylene.                                             

This example shows that the addition of the resin to the rubber inaccordance with the present invention raises the temperature at whichthe stock blows, and in addition, the temperature at which the stockburns.

Through the use of the present invention it is possible to preheat bymicrowave energy a rubber-resin stock approximately 100°F. higher beforeblow occurs. As a result cure time is markedly reduced.

The cure rates of stocks 13 and 18 at 275, 300, 325° and 350°F. wereexamined by obtaining Monsanto Rheometer curves which are shown in FIGS.2-3. It can be seen that in each instance the induction time for curingis markedly reduced.

EXAMPLE 8

Polyethylene and polypropylene were separately incorporated into astyrene-butadiene rubber along with other ingredients on a roll millwhich is maintained at a temperature of 330°F.

Sulfur and N-cyclohexyl-2-benzothiazylsulfenamide are added at 150°F.

    ______________________________________                                                    Stock 44  Stock 45  Stock 46                                      Compound    Parts     Parts     Parts                                         ______________________________________                                        SBR 1500.sup.1                                                                            100       100       100                                           Polyethylene          30                                                      Polypropylene                   30                                            Zinc oxide  3         3         3                                             Stearic Acid                                                                              2         2         2                                             Flexamine   1         1         1                                             Sulfur      1.75      1.75      1.75                                          Santocure   1.5       1.5       1.5                                           ______________________________________                                         .sup.1 (70/30 butadiene/styrene copolymer having a Mooney value ML-4 of       about 52)                                                                

Stocks 44 and 45 were cured 30 minutes at 307°F. and stock 46 was curedat 300°F. in a hot air oven. The change in density of each stock beforeand after cure was measured to determine the extent of blow. The resultsare as follows:

            Uncured Cured                                                                 Density Density   ρ.sub.a - ρ.sub.b                                                             × 100 (%)                                     ρ.sub.a (g/cc)                                                                    ρ.sub.b (g/cc)                                                                      (A)                                                 ______________________________________                                        Stock 44  0.7890    0.7305    -7.30                                           Stock 45  0.8249    0.7775    -5.76                                           Stock 46  0.8376     0.82073  -0.36                                           ______________________________________                                    

This example illustrates the unexpected result achieved by the use ofpolypropylene blended with rubber. An unmodified rubber and onecontaining polyethylene blended therein have a significant amount ofblow compared with the rubber-polypropylene blend.

EXAMPLE 9

This example discloses the fabrication of a rubber-resin blend into abelt which is free cured.

The ingredients of stock 47 were added to a Banbury and blended untilthe temperature of the batch 250°F. approximately.

The polypropylene and Surlyn A components of stock 48 were added to aBanbury which was preheated by steam, followed by subsequently mixing inthe remaining ingredients and blending until the temperature of thebatch reached 375°F.

Stock 47 was then blended with stock 48 on a mixing mill at 330°F. Also,stock 47 was milled at 330°F. before mixing with accelerators andsulfur. The curatives shown in Table 35 were added to these mixedcompounds at 200°F.

Table 34 shows the components of stocks 47 and 48.

                  Table 34                                                        ______________________________________                                        Compound           Parts                                                                       Stock 47 Stock 48                                            ______________________________________                                        Poly(butadiene-co-styrene)                                                    8454               52.86      52.86                                           Poly(butadiene-co-styrene)                                                    1606               36.89      36.89                                           Zinc Oxide         2.25       2.25                                            Chlorinated paraffin                                                                             2.25       2.25                                            Antisun wax        1.03       1.03                                            Stearic acid       .72        .72                                             N-Isopropyl-N'-phenyl-p-                                                      phenylene diamine  .81        .81                                             Thermoflex A       .47        .47                                             Plasticizer        .90        .90                                             Polypropylene                 27.32                                           Surlyn A (1555)               5.45                                            Total              98.18      130.95                                          ______________________________________                                    

                  Table 35                                                        ______________________________________                                                          Stock 49 Stock 50                                           ______________________________________                                        Stock 47            98.18      81.75                                          Stock 48                       16.33                                          N-cyclohexyl-2-benzothiazole-                                                 sulfenamide         .67        .67                                            Bismuth dimethyl-dithiocarbonate                                                                  .16        .16                                            Accelerator         .16        .16                                            Sulfur              .83        .83                                            Total               100.00     100.00                                         ______________________________________                                    

The stocks were free cured in hot air oven using the standard sycle, andsubsequently density measurements of the two stocks were taken. Theresults are given in Table 36.

                  Table 36                                                        ______________________________________                                        Determination of Extent of Blow by Measuring                                  Density                                                                       ______________________________________                                        Uncured Stock   Cured Stock ρ.sub.a - ρ.sub.b                                                             ×  100(%)                           ρ.sub.a (g/cc)                                                                            ρ.sub.b (g/cc)                                                                        ρ.sub.a                                       ______________________________________                                        Stock 49                                                                             1.1458       1.0066      -12.03                                        Stock 50                                                                             1.1331       1.1157      - 1.53                                        ______________________________________                                    

The physical properties of the stocks were measured. Table 37 gives theresults of said measurements.

                                      Table 37                                    __________________________________________________________________________    Physical Properties of Stocks 49-50                                                       Tensile                                                                            Tear                                                               Elongation                                                                          Strength                                                                           Strength      Adhesion                                       Stock %     (psi)                                                                              (Die C) (psi)                                                                         Durometer                                                                           (lbs./in.)                                     __________________________________________________________________________    Stock 49                                                                            300   1570 185     60    47-64                                                400   2240                                                              Stock 50                                                                            300   1910 192     67    50-48                                                400   2520                                                              __________________________________________________________________________

Stocks 49 and 50 were pressed with nylon fabrics treated withSBR-vinylpyridine latex at 250°F. for 4 minutes and cured completely inan oven (300°-320°F.) without pressure. Stock 50 did not blow, whilestock 49 did blow. In order to obtain no blow belts with stock 49 morethan 20 minutes press is required at 300°F. The result of adhesion ofstock 50 was as good (more than 50 psi) as normally press cured belting.

EXAMPLE 10

Polypropylene was initially added to polybutadiene at 340°F. usingmasterbatch blending technique at a ratio of 1 to 3. The masterbatchcompound was blended subsequently with polybutadiene at 270°F. in theamounts indicated. The filters, accelerators and curatives were added at200°F. The compositons (in parts) are set forth in Table 38:

                  Table 38                                                        ______________________________________                                        Compound       Stock 51  Stock 52  Stock 53                                   ______________________________________                                        Polybutadiene   100        100     83.33                                      Polypropylene  33.3                                                           Stock 51                           16.67                                      Precipitated hydrated      38      38                                         silica                                                                        Polyethylene               20      20                                         Titanox                    4       4                                          Barytes                    8       8                                          Dicumyl peroxide           2.75    2.75                                       Trimethylolpropane                                                            trimethacrylate            20      20                                         ______________________________________                                    

The compositions of stocks 52 and 53 were injected into a dimpled moldto form a golf ball. The balls were cured in a hot air oven. Thephysical properties of the ball are set forth in Table 39.

                  Table 39                                                        ______________________________________                                        Test           Stock 52     Stock 53                                          ______________________________________                                        Durometer      92           93                                                Tensile        1740 psi     2820 psi                                          Elongation     170%         160%                                              ______________________________________                                    

EXAMPLE 11

One sample prepared from stock 53 was cured in the microwave ovendescribed in Example 7. The time to cure was 5 minutes. Another samplewas cured using a standard cure cycle in a hot air oven which took 25minutes at 310°F.

In the foregoing examples the polypropylene used was either the typecoded 5820 manufactured by Shell Chemical Co. having a melt flow indexof 10-12, or the type coded 6723 manufactured by Hercules Chemical Co.having a melt flow index of 0.8-1.0.

EXAMPLE 12

This example discloses the critical necessity of maintaining theadditive polymer in the form of particles having a cross sectionaldimension not greater than one-half micron and a L/D ratio of 2 orgreater.

In order to eliminate the complexities of production compounds, a simple2 component system was employed for the purpose of this example.

A first compound labeled SWHR-3 was prepared by first placing standardMalaysian natural rubber on an oil heated mill, the roll surfacetemperature of which was maintained at 350°F. The natural rubber wasmilled for 5 minutes and subsequently cooled. Ten phr of polypropylene(Enjay Powder No. CD-481) which had been screened to include particlesof less than 100 mircons, was added to the natural rubber and themixture was blended for 5 minutes at a temperatre of 200° to 250°F.

A second compound (labeled SWHR-4) was prepared by milling a blend ofnatural rubber and 10 phr polypropylene (Enjay Powder No. CD-481,unscreened) for 5 minutes at 350°F. This blend was then cooled. Twocircular discs from each of the aforesaid compounds were formed fortesting. The discs were pressed for 3 minutes at a temperture between200° and 230°F. The pressed density (ρ_(p)) of each of the samples wasmeasured. The pressed sample was placed in an oven at a temperaturebetween 320° and 330°F. for 10 minutes to simulate a free cure. Thedensity (ρ_(c)) of the oven aged samples was then calculated. Table 40lists the values measured and calculated in accordance with theforegoing procedure.

                  TABLE 40                                                        ______________________________________                                                         Density  Density                                                              SWHR-3   SWHR-4                                              ______________________________________                                        Original (ρ.sub.p)                                                                           0.8728     0.8633                                          After Heating (ρ.sub.c)                                                                      0.7304     0.8599                                                    ρ.sub.c - ρ.sub.p                                           % Decrease  (    )         16.31%   0.39%                                               ρ.sub.p                                                         Appearance         Blow       No Blow                                         ______________________________________                                    

After the above noted compounds had been measured for density ratings,they were analyzed by transmissional electron microscopy whereupon itwas determined that the particles in the SWHR-4 sample possessed a crosssectional dimension not greater than one-half micron and an L/D ratio of2 or greater. The particles in the SWHR-3 compound did not have suchdimensions.

Table 40 demonstrates conclusively the necessity of having the additivepolymer present at a certain critical size configuration in order toachieve the no blow effect. Although the polypropylene added to theSWHR-3 compound was screened to obtain a particle size less than 100microns, the blending was performed at a temperature below the meltingpoint of the resin so that consequently the polypropylene in the blendwas not formed into particles having a cross sectional dimension notgreater than one-half micron and an L/D ratio of 2 or greater. As aresult the structure of SWHR-3 was a cellular or spongy appearance asopposed to the sample formed in accordance with the instant invention,i.e., SWHR-4 which has a continuous solid surface.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:
 1. A composition of matter comprising a blend ofvulcanizable material in admixture with between about 2-10% by weight ofa fiber forming, semi-crystalline, thermoplastic resin which possesses amelting point of 250°F. or greater, said resin being dispersed in saidvulcanizable material in the form of particles having a cross sectionaldimension (D) not greater than one-half micron and a length (L) to (D)ratio of 2 or greater.
 2. The composition of matter defined in claim 1wherein said vulcanizable material is selected from the group consistingof (a) diene polymers, (b) copolymer rubbers, (c) natural rubber, (d)depolymerized rubber and (e) interpolymers of at least 2 alphamonoolefins and at least one copolymerizable diene.
 3. The compositionof matter defined in claim 1 wherein said resin is selected from thegroup consisting of (a) polyolefins having 3-5 carbon atoms, (b)intra-and extra-linear polyamides, (c) polyester condensate products ofdihydric alcohols and organo-dibasic acids, (d) ionomers prepared byneutralizing with metal ions from Group I (a) and (b), Group II (a) and(b) or transition metals of the periodic table, at least 30% of the acidgroups of a copolymer of units derived from an alpha olefin of theformula R--CH=CH₂, wherein R is a hydrogen of alkyl group having 1-8carbon atoms and from 1.0 to 25 mole percent of units derived from analpha-beta ethylenically unsaturated carboxylic acid.
 4. The compositionof matter defined in claim 3 wherein said vulcanizable material isselected from the group consisting of polybutadiene, polychloroprene,polyisoprene, copolymers of isobutylene and between about 0.25 and 10%of isoprene, balata, Hevea rubber and rubbery interpolymers of at least2 alpha monoolefins having the formula CH₂ =CHR in which R is hydrogenor a saturated alkyl hydrocarbon radical having from 1-8 carbon atoms,and at least one copolymerizable diene selected from the groupconsisting of dicyclopentadiene, methylcyclopentadiene dimer, 1-4hexadiene, 11-ethyl-1, 11-tridecadiene-1, 9-octadiene-1,5-cyclooctadiene.
 5. The composition of matter defined in claim 4wherein said resin is selected from the group consisting ofpolypropylene, poly 4-methylpentene-1, polyethylene terephthalate, acopolymer of 75-99% by weight of acrylic or methyacrylic acid wherein atleast 30% of the acid groups have been neutralized with sodium, zinc orcalcium metal ions.